Define meaning of volunteer

I was driving past Weimar Fire Station when I saw a sign out front requesting “Volunteer Firemen Wanted.”
Does this mean they have to work for free? I wonder how many fire chiefs work for free? I know a lot of them don’t.
I heard one time that go-go dancers and truck drivers would work for free if they were asked to because they like their jobs so well.
KNIGHT WAGNER, Colfax